Out-of plane MEMS resonator with static out-of-plane deflection

Abstract

A residual stress gradient in a structural layer is employed to form a resonator deflected out of plane when at rest and the resulting strain gradient is utilized in out-of-plane transduction. Use of the strain gradient enables out-of-plane (e.g., vertical) transduction without yield and reliability problems due to stiction (e.g., the sticking of the resonator to the substrate) when the resonator is driven by an electrode to dynamically deflect out-of-plane. In particular embodiments, out-of-plane transduction is utilized to achieve better transduction efficiency as compared to lateral resonator designs of similar linear dimensions (i.e. footprint) results in a lower motional resistance.

1. A MEMS device comprising:
 a resonator coupled to a substrate, the resonator including a strain gradient statically deflecting a first portion of the resonator; and 
 a driver configured to drive the resonator in a resonant mode which varies the amount of deflection; 
 wherein the resonator comprises:
 a cantilever beam; and 
 a first plurality of lattice beams extending along a length of the cantilever beam. 
 
 
     
     
       2. The MEMS device as in  claim 1 , wherein the driver comprises at least one of: electrostatic transducer, piezoelectric transducer, an optical transducer or a thermal transducer configured to provide a driving force to the resonator in the direction of the deflection. 
     
     
       3. The MEMS device as in  claim 1 , wherein the driver includes an electrode physically coupled to the substrate. 
     
     
       4. The MEMS device as in  claim 3 , wherein a second portion of the resonator remains in a plane of the electrode when the first portion is statically deflected above or below the plane of the electrode. 
     
     
       5. The MEMS device as in  claim 3 , wherein the electrode is of one or more electrodes positioned relative to the resonator to provide an approximately zero net electrostatic force in the plane of the electrode(s) and to provide a non-zero net force out of the plane. 
     
     
       6. The MEMS device as in  claim 1 , wherein the strain gradient elevates a surface of a tip of the cantilever beam above a plane defined by a top surface of an electrode of the driver. 
     
     
       7. The MEMS device as in  claim 1 , wherein a surface along a length of the resonator is spaced apart from a surface of an electrode of the driver to form a gap which is to remain substantially constant when the resonator is driven. 
     
     
       8. The MEMS device as in  claim 1 , wherein the resonator has a thickness to width ratio less than one. 
     
     
       9. The MEMS device as in  claim 1 , wherein the resonator is adjacent to two dimensions of a perimeter of an electrode of the driver. 
     
     
       10. The MEMS device as in  claim 9 , wherein the gap between the resonator and the two dimensions of the electrode perimeter are to both remain approximately constant when the resonator is driven. 
     
     
       11. The MEMS device as in  claim 1 , wherein the resonator further comprises:
 a first material with a first coefficient of thermal expansion (CTE); and 
 a second material with a second CTE. 
 
     
     
       12. The MEMS device as in  claim 1 , further comprising:
 a second plurality of lattice beams extending along the length of the cantilever beam, 
 wherein an anchor of the cantilever beam is between the first plurality of lattice beams and the second plurality of lattice beams. 
 
     
     
       13. The MEMS device as in  claim 12 , wherein the cantilever beam is anchored between first and second tips of the cantilever beam at approximately a midpoint of the cantilever beam. 
     
     
       14. The MEMS device as in  claim 12 , further comprising a secondary beam coupled orthogonally to the cantilever beam, the secondary beam being anchored at a first tip of the secondary beam and a second tip of the secondary beam. 
     
     
       15. The MEMS device as in  claim 12 , wherein the first plurality of lattice beams are replicated on both sides of the width of the cantilever beam. 
     
     
       16. The MEMS device as in  claim 1 , wherein the resonator further comprises a resonant frequency tuning plate positioned over a tuning electrode embedded in the substrate. 
     
     
       17. The MEMS device as in  claim 1 , wherein the resonator further comprises:
 a first material with a first Young's modulus dependence on temperature; and 
 a second material with a second Young's modulus dependence on temperature. 
 
     
     
       18. The MEMS device as in  claim 17 , wherein the first material has a negative Young's modulus dependence on temperature and the second material has a positive Young's modulus dependence on temperature. 
     
     
       19. The MEMS device as in  claim 18 , wherein the first material is a semiconductor and the second material is a dielectric. 
     
     
       20. The MEMS device as in  claim 19 , wherein the semiconductor comprises at least one of silicon and germanium and the dielectric comprises silicon dioxide. 
     
     
       21. The MEMS device as in  claim 17 , wherein the second material is contained within a trench in the first material. 
     
     
       22. A MEMS device comprising:
 a resonator coupled to a substrate, the resonator including a strain gradient statically deflecting a first portion of the resonator; and 
 a driver configured to drive the resonator in a resonant mode which varies the amount of deflection, 
 wherein the resonator is adjacent to two dimensions of a perimeter of an electrode of the driver, 
 wherein the resonator comprises a plurality of lattice beams forming a lattice along a length of the resonator, wherein a subset of the lattice beams form a lattice opening perimeter surrounding the electrode. 
 
     
     
       23. The MEMS device as in  claim 22 , wherein the electrode is one of a plurality and the lattice beams form lattice opening perimeters about each of the plurality of electrodes. 
     
     
       24. The MEMS device as in  claim 23 , wherein the perimeters have a total length that is at least an order of magnitude larger than the length of a cantilever to which the lattice beams are attached. 
     
     
       25. The MEMS device as in  claim 24 , further comprising a plurality of sense electrodes, wherein the resonator further comprises a plurality lattice beams forming perimeters about each of the plurality of sense electrodes. 
     
     
       26. A MEMS device, comprising:
 a substrate; and 
 a resonator coupled to the substrate, wherein the resonator comprises a plurality of lattice beams forming a lattice along a length of the resonator, wherein a subset of the lattice beams form a perimeter surrounding an electrode, 
 wherein the resonator has a strain gradient statically deflecting a first portion of the resonator away from the substrate. 
 
     
     
       27. The MEMS device as in  claim 26 , further comprising a plurality of electrodes, wherein the resonator further comprises a plurality of lattice beams forming perimeters about each of the plurality of electrodes. 
     
     
       28. The MEMS device as in  claim 26 , wherein the resonator comprises:
 a cantilever beam, the plurality of lattice beams extending along a length of the cantilever beam. 
 
     
     
       29. The MEMS device as in  claim 28 , wherein the plurality of lattice beams are replicated on both sides of the width of the cantilever beam. 
     
     
       30. The MEMS device as in  claim 28 , wherein the resonator further comprises:
 a second plurality of lattice beams extending along the length of the cantilever beam, 
 wherein an anchor of the cantilever beam is between the first plurality of lattice beams and the second plurality of lattice beams. 
 
     
     
       31. A method of operating a MEMS resonator, the method comprising:
 causing a resonator to resonate in a torsional mode by providing a drive electrode with an AC signal, wherein a drive capacitance is substantially linear with dynamic displacement of the resonator and wherein the resonator includes a strain gradient statically deflecting the resonator in a direction substantially parallel with the direction of dynamic displacement; and 
 detecting, with a sense electrode, a response based on the resonance of the resonator. 
 
     
     
       32. The method as in  claim 31 , wherein the resonator is driven to resonate in a direction normal to a substrate to which the resonator is anchored. 
     
     
       33. The method as in  claim 31 , wherein the magnitude of maximum dynamic displacement is less than the magnitude of maximum static displacement. 
     
     
       34. The method as in  claim 31 , wherein the electrode is one of a plurality to provide an approximately zero net electrostatic force in the plane of the electrode(s) and to provide a non-zero net force out-of-plane.